Safety Switch for Photovoltaic Systems

ABSTRACT

Various implementations described herein are directed to a methods and apparatuses for disconnecting, by a device, elements at certain parts of an electrical system. The method may include measuring operational parameters at certain locations within the system and/or receiving messages from control devices indicating a potentially unsafe condition, disconnecting and/or short-circuiting system elements in response, and reconnection the system elements when it is safe to do so. Certain embodiments relate to methods and apparatuses for providing operational power to safety switches during different modes of system operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.17/240,276, filed Apr. 26, 2021, entitled “Safety Switch forPhotovoltaic Systems,” which is a continuation of U.S. application Ser.No. 16/248,475, filed Jan. 15, 2019, now U.S. Pat. No. 11,018,623,issued May 25, 2021 entitled “Safety Switch for Photovoltaic Systems,”which is a continuation-in-part of U.S. nonprovisional application Ser.No. 15/250,068, filed Aug. 29, 2016, now U.S. Pat. No. 10,230,310,issued Mar. 12, 2019, entitled “Safety Switch for Photovoltaic Systems.”The content of these are incorporated by reference herein in theirentireties for all purposes. The present application claims priority toU.S. provisional patent application Ser. No. 62/318,303, filed Apr. 5,2016, entitled “Optimizer Garland,” hereby incorporated by reference inits entirety. Additionally, the present application claims priority toU.S. provisional patent application Ser. No. 62/341,147, filed May 25,2016, entitled “Photovoltaic Power Device and Wiring,” herebyincorporated by reference in its entirety.

BACKGROUND

Safety regulations may require disconnecting and/or short-circuiting oneor more photovoltaic (PV) generators or other components in case of anunsafe condition occurring in a photovoltaic installation. For example,safety regulations require that in case of an unsafe condition (e.g. afire, a short-circuit, carrying out of maintenance work), the maximumvoltage at any point in a photovoltaic installation may not exceed asafe voltage level. In some photovoltaic systems, it may be necessary todisconnect and/or short-circuit one or more photovoltaic generator(s) toachieve the safe voltage requirement. While photovoltaic systems may bedeployed for tens of years, safety regulations may change at shortertime intervals (e.g. every several years). It would be advantageous tohave a controllable safety switch which may be controlled to disconnector short-circuit a PV generator in case of a safety hazard, and whichmay be controlled to reconnect the photovoltaic generator once thesystem is safe again. It would be desirable for controllable safetyswitches to be cost-effective and easily deployed.

SUMMARY

The following summary is a short summary of some of the inventiveconcepts for illustrative purposes only, and is not intended to limit orconstrain the inventions and examples in the detailed description. Oneskilled in the art will recognize other novel combinations and featuresfrom the detailed description.

Embodiments herein may employ safety switches and associated apparatusesand methods for controlling currents through branches and/or voltages atnodes in photovoltaic (PV) installations.

In illustrative embodiments comprising one or more electrical systems, agroup of electrical safety switches may be electrically connectable to aplurality of electrical power sources. The electrical safety switchesmay be controllable to maintain safe operation of the electricalsystems.

In illustrative electrical systems, a safety switch may be deployedbetween serially-connected photovoltaic generators in a photovoltaicinstallation. In some embodiments, safety switches may be installedbetween each pair of PV generators. In some embodiments, the number andlocation of safety switches may be chosen with regard to current safetyregulations, and in some embodiments, the number and location of safetyswitches may be chosen with regard to anticipated “worst-case” safetyregulations. For example, in locales where adding, reconfiguring and/orremoving system components is easy and inexpensive, safety switches maybe deployed in a PV installation in accordance with the safetyregulations at the time the installation was built. In locales whereadding, reconfiguring and/or removing system components may be difficultor expensive, safety switches may be deployed in a manner that complieswith a “worst-case” (i.e. most stringent) prediction of futureregulations.

Illustrative safety switches according to some embodiments may beretrofit to existing photovoltaic installations and components.Illustrative safety switches according to some embodiments may beintegrated in other PV system components (e.g. connectors, PVgenerators, power devices, combiner boxes, batteries and/or inverters),potentially reducing the cost of design and manufacturing of the safetyswitches, and increasing

In some embodiments, auxiliary power circuits are used to provide powerto safety switches and associated controllers. In some embodiments,safety switches are located at system points which do not carrysignificant electrical power when the safety switches are in aparticular state (e.g., when safety switches are in the ON state).Illustrative auxiliary power circuits are disclosed herein, along withassociated methods for providing power to the auxiliary power circuitsand safety switches regardless of the state of the safety switches.

In some embodiments, components and design of safety switches may beselected to regulate or withstand electrical parameters whenillustrative safety switches are in the ON or OFF states. For example,some illustrative safety switches may comprise shunt resistors sized toregulate electrical current flowing through safety switches when thesafety switches are in the OFF position.

Further embodiments include photovoltaic power devices comprisinginternal circuitry configured to limit a voltage between input terminalsto the photovoltaic power devices in case of a potentially unsafecondition while continuously providing operational power to thephotovoltaic power devices.

Further embodiments include electrical circuits for interconnectingphotovoltaic generators and photovoltaic power devices configured tolimit a voltage between various system nodes while continuouslyproviding operational power to the photovoltaic power devices.

Further embodiments include a chain of preconnected photovoltaic powerdevices with associated safety switches, which may provide acost-effective, easy way to wire a photovoltaic generation system alongwith associated safety switches.

In some embodiments, safety switches may be in communication withaccompanying system devices, such as system control devices and/orend-user devices such as graphical user interfaces for monitoringapplications.

Further embodiments include user interfaces for monitoring the state ofand parameters measured by safety switches in illustrative powersystems. A system owner or operator may be able to view a list of systemsafety switches, associated switch states and electrical parametermeasured thereby. In some embodiments, the list may be a graphical userinterface (GUI) viewable on a computing device, such as a computermonitor, tablet, smart-television, smartphone, or the like. In someembodiments, the system operator may be able to manually control safetyswitches (e.g. by pressing buttons).

As noted above, this Summary is merely a summary of some of the featuresdescribed herein and is provided to introduce a selection of concepts ina simplified form that are further described below in the DetailedDescription. The Summary is not exhaustive, is not intended to identifykey features or essential features of the claimed subject matter and isnot to be a limitation on the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, claims, and drawings. The present disclosure is illustratedby way of example, and not limited by, the accompanying figures.

FIG. 1A illustrates a photovoltaic system configuration according tovarious aspects of the present disclosure.

FIG. 1B illustrates a photovoltaic system configuration according tovarious aspects of the present disclosure.

FIG. 2 illustrates part of a photovoltaic system configuration accordingto various aspects of the present disclosure.

FIG. 3 illustrates a safety switch according to various aspects of thepresent disclosure.

FIGS. 4A-4B illustrate a safety switch according to various aspects ofthe present disclosure.

FIG. 5A illustrates part of a photovoltaic system configurationaccording to various aspects of the present disclosure.

FIG. 5B illustrates a photovoltaic generator according to variousaspects of the present disclosure.

FIG. 6 illustrates a method for operating a safety switch according tovarious aspects of the present disclosure.

FIGS. 7A-7C illustrate circuits for providing operational power to asafety switch according to various aspects of the present disclosure.

FIG. 7D illustrates a timing diagram depicting some of the operationalparameters of a safety switch according to various aspects of thepresent disclosure.

FIG. 7E illustrates a circuit for providing operational power to asafety switch according to various aspects of the present disclosure.

FIG. 7F illustrates a timing diagram depicting some of the operationalparameters of a safety switch according to various aspects of thepresent disclosure.

FIG. 7G illustrates a circuit for providing operational power to asafety switch according to various aspects of the present disclosure.

FIG. 7H illustrates a circuit for providing operational power to asafety switch according to various aspects of the present disclosure.

FIG. 7I illustrates part of an illustrative datasheet indicatingpossible operating points for operating a transistor according tovarious aspects of the present disclosure.

FIG. 8 illustrates a photovoltaic system configuration according tovarious aspects of the present disclosure.

FIG. 9 illustrates a photovoltaic power device according to variousaspects of the present disclosure.

FIG. 10 illustrates a photovoltaic system configuration according tovarious aspects of the present disclosure.

FIGS. 11A-11B illustrate a photovoltaic power devices according tovarious aspects of the present disclosure.

FIG. 12 illustrates a photovoltaic system configuration according tovarious aspects of the present disclosure.

FIG. 13A illustrates circuitry of a safety switch according to variousaspects of the present disclosure.

FIG. 13B illustrates circuitry of a photovoltaic power device accordingto various aspects of the present disclosure.

FIG. 14 illustrates a portion of a chain of photovoltaic power devicesaccording to various aspects of the present disclosure.

FIG. 15 is an illustrative mockup of a user interface for an electricalsystem according to illustrative embodiments.

FIG. 16 illustrates a photovoltaic power device according to variousaspects of the present disclosure.

DETAILED DESCRIPTION

In the following description of various illustrative embodiments,reference is made to the accompanying drawings, which form a parthereof, and in which is shown, by way of illustration, variousembodiments in which aspects of the disclosure may be practiced. It isto be understood that other embodiments may be utilized and structuraland functional modifications may be made, without departing from thescope of the present disclosure.

Reference is now made to FIG. 1A, which shows a photovoltaic (PV) systemaccording to illustrative embodiments. PV system 100 may comprise aplurality of PV strings 104 coupled in parallel between a ground bus anda power bus. Each of PV strings 104 may comprise a plurality ofserially-connected PV generators 101 and a plurality of safety switches102. PV generators 101 may comprise one or more photovoltaic cells(s),module(s), panel(s) or shingle(s). In some embodiments, PV generators101 may be replaced by direct current (DC) batteries or alternativedirect current or alternating current (AC) power sources.

In the illustrative embodiment of FIG. 1A, a safety switch 102 isdisposed between each pair of PV generators 101. In some embodiments(e.g. the embodiment shown in FIG. 2 ) a safety switch 102 may bedisposed between groups of more than one serially-connected PVgenerators. Safety switch 102 may comprise a control device and acommunication device, and may be operated to disconnect adjacent PVgenerators when receiving (e.g. via the communication device) a commandto disconnect PV generators.

In some embodiments, the power and ground buses may be input to systempower device 110. In some embodiments, system power device 110 mayinclude a DC/AC inverter and may output alternating current (AC) powerto a power grid, home or other destinations. In some embodiments, systempower device 110 may comprise a combiner box, transformer and/or safetydisconnect circuit. For example, system power device 110 may comprise aDC combiner box for receiving DC power from a plurality of PV strings104 and outputting the combined DC power. In some embodiments, systempower device 110 may include a fuse coupled to each string 104 forovercurrent protection, and/or one or more disconnect switches fordisconnecting one or more PV strings 104.

In some embodiments, system power device 110 may include or be coupledto a control device and/or a communication device for controlling orcommunicating with safety switches 102. For example, system power device110 may comprise a control device such as a microprocessor, DigitalSignal Processor (DSP) and/or a Field Programmable Gate Array (FPGA)configured to control the operation of system power device 110. In someembodiments, system power device 110 may comprise multiple interactingcontrol devices. System power device 110 may further comprise acommunication device (e.g. a Power Line Communication circuit and/or awireless transceiver) configured to communicate with linkedcommunication devices included in safety switches 102. In someembodiments, system power device 110 may comprise both a control deviceand a communication device, the control device configured to determinedesirable modes of operation for PV power devices (e.g. power devices103), and the communication device configured to transmit operationalcommands and receive reports from communication devices included in thePV power devices.

System power device 110 may be coupled to any number of other devicesand/or systems such as PV systems 100 (e.g., various discrete and/orinterconnected devices such as disconnect(s), PV cell(s)/array(s),inverter(s), micro inverter(s), PV power device(s), safety device(s),meter(s), breaker(s), AC main(s), junction box(es), camera etc.),network(s)/Intranet/Internet, computing devices, smart phone devices,tablet devices, camera, one or more servers which may include data basesand/or work stations. System power device 110 may be configured forcontrolling the operation of components within PV system 100 and/or forcontrolling the interactions with other elements coupled to PV system100.

In some embodiments, the power and ground buses may be further coupledto energy storage devices such as batteries, flywheels or other energystorage devices.

Safety regulations may define a maximum allowable voltage between theground bus and any other voltage point in PV system 100, during bothregular operating conditions and during potentially unsafe conditions.Similarly, safety regulations may define a maximum allowable voltagebetween any two voltage points in PV system 100. In some scenarios, anunsafe condition in PV system 100 may require disconnecting orshort-circuiting one or more of the PV generators 101 in a PV string104.

As a numerical example, an illustrative PV string 104 may comprise 20serially-connected PV generators 101. Each PV generator 101 may have anopen-circuit voltage of 45V. In case of an unsafe condition (e.g. afire, detection of an arc or a dangerous short-circuit somewhere in PVsystem 100), safety regulations may require that system power device 110cease drawing power from PV string 104, resulting in an open-circuitvoltage of 45·20=900V across PV string 104. Safety regulations mayfurther require that in case of an unsafe condition, the maximum voltagebetween any two points in PV system 100 may not exceed, for example,80V. To comply with safety regulations, safety switches 102 maydisconnect the plurality of PV generators 101 comprising PV string 104,resulting in PV generators 101 (excluding the PV generators 101 coupledto the ground and power buses) having a “floating” voltage with regardto ground, and a voltage drop of about 45V between the two terminals ofeach PV generator.

In some embodiments, system power device 110 may respond to apotentially unsafe system condition by limiting the voltage across eachPV string 104. For example, system power device 110 may comprise aninverter configured to regulate a voltage of about 60V across each PVstring 104 in case of a potentially unsafe condition.

Reference is now made to FIG. 1B, which illustrates a single PV string104 coupled to system power device 110. In case of a potentially unsafesystem condition, safety switches 102 may disconnect (i.e. each switchmay move to the OFF state), and system power device 110 may apply avoltage to PV string 104. In the numerical example of FIG. 1B, each PVgenerator is assumed to be operating at an open-circuit voltage of 45V,and system power device 110 may apply a voltage of 60V across PV string104. Safety switches 102, in accordance with embodiments disclosedherein, may be configured to provide and withstand a voltage drop ofopposite polarity to the PV generators. In the numerical example of FIG.1B, PV string 104 comprises twenty PV generators 101 and twenty safetyswitches 102. Each PV generator has a positive voltage drop of 45V, andeach safety switch 102 has a negative voltage drop of 42V, providing astring voltage of (45−42)·20=60V. It may be noted that the voltage dropbetween each pair of locations in the PV system does not exceed 60V.

It is to be noted that the ratio of photovoltaic generators to safetyswitches, and the location of safety switches, may change depending onelectrical parameters of photovoltaic generators and safety regulations.For example, if low-voltage PV generators (e.g. PV generators having anopen-circuit voltage of 10V) are used as PV generators 101, and safetyregulations allow a maximum point-to-point voltage of 55V in case of apotentially unsafe condition, a single safety switch 102 may be disposedper five PV generators 101. If safety regulations are changed to allow amaximum point-to-point voltage of 45V in case of a potentially unsafecondition, additional safety switches 102 may be added.

Safety switches 102 may comprise a resistor for regulating currentthrough safety switches 102 when the switches are in the OFF state. Forexample, each of safety switches 102 may comprise a shunt resistor (e.g.resistor R31 of FIG. 3 ) having a resistance of about 11 kΩ, to regulatethe OFF-state current to be about 42V/1 kΩ=42 mA. In general, the valueof a shunt resistor may vary according to expected OFF-state voltagesand currents, and may be between 10Ω and 5 kΩ.

In some embodiments, the values may vary depending on the regulatedvoltage provided by system power device 110 and the open-circuit voltageof each PV generator 101. For example, string 104 may comprise ten PVgenerators, and ten safety switches, each PV generator having anopen-circuit voltage of 30V, and system power device 110 may provide avoltage of 50V across PV string 104. In that case, each safety switchmay be operated to have a negative voltage of 25V, providing the stringvoltage of (30−25)·10=50V.

Reference is now made to FIG. 2 , which shows a photovoltaic stringaccording to illustrative embodiments. PV string 204 may comprise aplurality of PV generators 101 and safety switches 102. PV generators101 may be similar to or the same as PV generators 101 of FIG. 1A, andsafety switches 102 may be similar to or the same as safety switches 102of FIG. 1 . Safety switches 102 may be installed between each pair of PVgenerators 101, such that each PV generator 101 (excluding the PVgenerators connected to the ground and power buses) has a first terminalconnected to a different PV generator 101 and a second terminalconnected to a safety switch 102. The arrangement illustrated in FIG. 2may be appropriate in systems where the maximum allowed safe voltage isgreater than or equal to double the open-circuit voltage of a single PVgenerator 101. For example, if each PV generator 101 has an open-circuitvoltage of 45V and the maximum allowed safe voltage is 100V, or each PVgenerator 101 has an open-circuit voltage of 30V and the maximum allowedsafe voltage is 80V, the arrangement illustrated in FIG. 2 may reducecosts by reducing the required number of safety switches while stillcomplying with safety regulations.

Reference is now made to FIG. 3 , which illustrates a safety switchaccording to illustrative embodiment. Safety switch 302 may be used assafety switch 102 in FIG. 1A and FIG. 2 . Safety switch may comprisemale connector 306 and female connector 307, male connector 306 designedto fit a female connector features by a PV generator (e.g. PV generator101) and female connector 307 designed to fit a male connector featuresby a PV generator. Conductor 308 may provide an electrical connection tomale connector 306, and conductor 309 may provide an electricalconnection to female connector 307. In some embodiments, variousinterconnecting connectors may be used. Safety switch 302 may include aswitching element disposed between conductor 308 and conductor 309. Inthe illustrative embodiment of FIG. 3 , transistor Q1 may be used as aswitching element disposed between conductor 308 and conductor 309.Safety switch 302 may further include controller 303 for controlling theoperation of transistor Q1. Transistor Q1 may be realized using variouselectrical devices, such as Metal-Oxide-Semiconductor Field EffectTransistor (MOSFET), Insulated Gate Bipolar Junction transistor (IGBT),Bipolar Junction Transistor (BJT), Junction gate field-effect transistor(JFET) or other appropriate devices. In some embodiments, transistor Q1may be realized using multiple transistors connected in parallel, toimprove electrical performance (e.g. to reduce losses). In theillustrative embodiments disclosed herein, transistor Q1 and similarswitching elements will be assumed to be MOSFETs comprising a bodydiode. Diode D31 may be the body diode of transistor Q1. In someembodiments (e.g. in case Q1 is a MOSFET comprising a low-quality bodydiode) a separate diode may be coupled in parallel to diode D31 tofunction as an alternative bypass diode. Diode D31 may be oriented toprevent forward bias of diode D31 when the transistor is in the OFFposition. Resistor R31 may be disposed across the terminals oftransistor Q1. Resistor R31 may be sized to regulate the OFF-stateresistance across the terminals of transistor Q1. For example, if theanticipated OFF-state voltage drop across transistor Q1 is 40V, and thedesired OFF-state leakage current through safety switch 302 is 20 mA,R31 may be about 40V/20 mA=2000Ω. In some embodiments, R31 might not befeatured (e.g. if there is no need or desire to regulate the OFF-stateleakage current).

Safety switch 302 may comprise communication device 305 forcommunicating with other devices and controller 303 for controlling theoperation (e.g. turning ON and OFF) of transistor Q1. Controller 303 maybe an analog circuit, microprocessor, Digital Signal Processor (DSP),Application-Specific Integrated Circuit (ASIC) and/or a FieldProgrammable Gate Array (FPGA). In some embodiments, communicationdevice 305 may receive a command from an external device to change thestate of transistor Q1, and communication device 305 may convey thecommand to controller 303. Communication device 305 may communicate withexternal devices using various technologies such as Power LineCommunications (PLC), acoustic communications transmitted overconductors 308 and 309, and wireless communication protocols (e.g.Wi-Fi™, ZigBee™, Bluetooth™, cellular communications, etc.).

Auxiliary power circuit 304 may be coupled to conductors 308 and/or 309,and may provide power to controller 303, sensor/sensor interface(s) 310and/or communication device 305. Auxiliary power circuit 304 may bevariously realized, with illustrative embodiments disclosed herein (e.g.in FIGS. 7A-7C, 7E, 7H). In some embodiments, two or more of controller303, auxiliary power circuit 304 and communication device 305 may beintegrated as a single unit. For example, in FIG. 7C, communicationdevice 305 may receive a PLC signal which also provides power tocontroller 303.

In some embodiments, safety switch 302 may further comprise measurementsensor(s) and/or sensor interface(s) 310 for measuring parameters suchas current, voltage and/or temperature. For example, sensor/sensorinterface(s) 310 may include a current sensor for measuring the currentthrough conductor 308 or conductor 309, and/or a voltage sensor formeasuring the voltage drop across transistor Q1, and/or a temperaturesensor for measuring the temperature at or near male connector 306,female connector 307 and/or transistor Q1. In some embodiments,sensor(s)/sensor interface(s) 310 may provide measurements to controller303, with controller 303 configured to take action (e.g. change thestate of transistor Q1) according to the measurements received. Forexample, controller 303 may be configured to set the state of Q1 to OFFif a high current is measured through conductor 309, or if a hightemperature is measured near male connector 306. In some embodiments,controller 303 may provide the measurements obtained fromsensor(s)/sensor interface(s) 310 to communication device 305, withcommunication device 305 configured to transmit the measurements to asystem controller or data-collection device (not explicitly depicted),such as system power device 110 of FIG. 1 . In some embodiments,sensor(s)/sensor interface(s) 310 may provide measurements directly tocommunication device 305, bypassing controller 303.

It should be noted that while a preferred embodiment of the disclosureincludes providing transistor Q1 for safety features (e.g. the abilityto disconnect two PV generators from each other), other embodimentsincluded herein might not include transistor Q1. Sensor/sensorinterface(s) 310, auxiliary power circuit 304 and communication device305 may be combined to provide measurement and data-reporting featureseven without the safety advantages (e.g. ability to disconnect aphotovoltaic generator) provided by safety transistor Q1.

Reference is now made to FIGS. 4A-4B, which illustrates the connectivityof a safety switch according to illustrative embodiments. Safety switch402 may be similar to or the same as safety switch 302 of FIG. 3 .Safety switch 402 may comprise male connector 406 for connecting toconnector 403, with connector 403 connected to conductor 404 whichcarries power generated by a first PV generator (not explicitlydepicted). Similarly, safety switch 402 may comprise female connector407 for connecting to connector 408, with connector 408 connected toconductor 409 which carries power generated by a second PV generator(not explicitly depicted). In some conventional photovoltaic systems,the first and second photovoltaic generators may be serially connectedby connecting connector 403 to connector 408. Safety switch 402 may bedesigned to seamlessly connect to connector 403 on one end and toconnector 408 on the other end, adding safety-disconnect, control and/ormonitoring features to a photovoltaic installation, either duringconstruction of the installation or as a retrofit feature at a latertime.

FIG. 4A shows safety switch 402 along with connectors 408 and 403 priorto connecting, according to illustrative embodiments, while FIG. 4Bshows connection point 400 comprising safety switch 402 connected toconnectors 408 and 403 (the component boundaries indicated by dashedlines).

In some embodiments, advantages may be obtained by integrating safetyswitch 402 into a photovoltaic generator connector or a PV generatorjunction box. For example, safety switch 402 may be built into connector403 or connector 408 of a PV generator, providing safety switchingfunctionality in a PV generator without necessitating additionalcomponents and connections. Integrating safety switches in PV generatorconnectors or junction boxes may reduce costs (e.g. by not requiring aseparate enclosure and connectors for the safety switch) and simplifyinstallation (since no additional components need be connected).

Reference is now made to FIG. 5A, which shows part of a photovoltaic(PV) string featuring a safety switch according to illustrativeembodiments. PV string 500 may be part of a string of PV generators 101(e.g. part of a string similar to or the same as PV string 104 of FIG.1A, comprising generators similar to or the same as PV generators 101 ofFIG. 1A and FIG. 2 ) connected to each other via connection points 400.Connection points 400 may be similar to or the same as connection point400 of FIG. 4A and FIG. 4B, and may include a safety switch (e.g. safetyswitch 402) coupled in between two PV generator connectors (e.g.connectors 403 and 408). Each PV generator 101 may comprise conductors404 and 409 for carrying photovoltaic power from PV cells comprising thePV generator, and connectors 403 and 408 for connecting to safety switch402.

Reference is now made to FIG. 5B, which illustrates a PV generatorcomprising a safety switch according to illustrative embodiments. PVgenerator 101 may comprise junction box 511 and conductors 404 and 409.FIG. 5B may illustrate the back side on a PV generator, with PV cellsmounted on the front side of the PV generator (not explicitly shown). Insome embodiments, PV cells may be mounted on both sides of the PVgenerator, or the back side of the PV generator may be constructed toallow solar irradiance to reach the PV cells from both sides of the PVgenerator. Junction box 511 may comprise electrical connections 512 and513 for collecting photovoltaic power from the PV cells, and providingthe photovoltaic power via conductors 409 and 404.

In illustrative embodiments disclosed herein, safety switch 502 may bedisposed between conductor 404 and electrical connection 512. Safetyswitch 502 may be functionally similar or the same as safety switch 302of FIG. 3 , without requiring the physical enclosure and connectors 306and 307. Transistor Q1, diode D31, sensor(s)/sensor interfaces 510,controller 503, communication device 505 and/or auxiliary power circuit504 may be integrated in junction box 511. In some embodiments, aresistor may be coupled across the terminals of transistor Q1 (similarlyto resistor R31 of FIG. 3 ) for regulating the OFF-state current throughsafety switch 502. In some embodiments, auxiliary power circuit 504 maybe coupled between conductors 404 and 409 for receiving photovoltaicpower generated by PV generator 101, and may provide power to controller503, communication device 505 and/or sensor(s)/sensor interfaces 510.

In some embodiments, junction box 511 may further include an integratedPV power device similar to or the same as PV power device 903 of FIG. 9. PV power device 903 may be coupled between conductors 404 and 409 andelectrical connections 512 and 513. For example, power converter 900 ofFIG. 9 may receive power from electrical connections 512 and 513, andmay output power to conductors 404 and 409. Safety switch 502 may bedisposed between PV power device 903 and electrical connection 512, or,in some embodiments, may be integrated into PV power device 903.

Reference is now made to FIG. 6 , which shows a method for operating asafety switch (e.g. safety switch 102 of FIG. 1A, safety switch 302 ofFIG. 3 ). Method 600 may be carried out by a controller similar to orthe same as controller 303 of FIG. 3 . At step 601, the initialcondition may be that the switch is in the ON state, allowing current toflow between the two conductors coupled to the switch (e.g. conductors404 and 409 of FIG. 5A). During step 601, an auxiliary power circuitcoupled to the safety switch may provide power to the controller and/ora gate driver for maintaining the switch in the ON state (for example,some types of transistors implementing safety switches may be “normallyOFF”, in which case the auxiliary power circuit may power a voltagesignal applied to a transistor gate node to maintain the ON state). Atstep 602, the controller may receive a command to turn the switch to theOFF state. In some embodiments, the command may be received via acommunication device (e.g. communication device 305) in communicationwith a system control device. In some embodiments, at step 602, insteadof receiving a command to turn the switch to the OFF state, thecontroller may independently determine that an unsafe condition may bepresent (e.g. due to sensor reporting high current or temperature, or asensor detecting a rapid change in current flowing through the switch,or based on comparing two electrical parameters and detecting asubstantial mismatch) and determine that the switch should be turned tothe OFF state. In some embodiments, a determination that the switchshould be turned to the OFF state may be made in response to notreceiving a signal. For example, in some illustrative systems, a systemcontrol device continuously provides a “keep alive” signal to associatedsafety switches and PV power devices. Not receiving a “keep alive”signal may indicate a potentially unsafe condition and may cause adetermination that the switch should be turned to the OFF state.

Still referring to FIG. 6 , at step 603, the controller turns the switchto the OFF state. In some embodiments (e.g. if the switch is a “normallyON” transistor), turning the switch to the OFF state may includeapplying a voltage to a transistor terminal, and in some embodiments(e.g. if the switch is a “normally OFF” transistor), turning the switchto the OFF state may include ceasing to apply a voltage to a transistorterminal. At step 604, the controller waits to receive a command to turnthe switch back to the ON position. Generally, once an unsafe conditionhas been resolved, a system control device may provide a signalindicating that it is safe to reconnect PV generators and to resumeproviding power. In some embodiments, at step 604 the controller mayindependently determine that it is safe to return the switch to the ONposition (e.g., due to a sensor reporting that the unsafe condition isno longer present).

At step 605, the controller determines if a command (or, in someembodiments, a self-determination) to turn the switch to the ON statehas been received. If no such command (or determination) has beenreceived, the controller carrying out method 600 returns to step 604. Ifa command (or, in some embodiments, a self-determination) to turn theswitch to the ON state has been received, the controller carrying outmethod 600 proceeds to step 606, turns the switch back to the ON state(e.g. by applying a voltage to a transistor node, or removing an appliedvoltage from a transistor node) and returns to step 601.

An auxiliary circuit for providing continuous power supply to a safetyswitch according to embodiments disclosed herein may be variouslyimplemented. Auxiliary power circuits may provide power for operating asafety switch under varying conditions and at various times. Forexample, auxiliary power circuits may provide operational power to asafety switch at three times: at initial startup (i.e. when the systemcomprising a safety switch is first deployed), at steady-state ON time(i.e. when the system is up and running, during normal operatingconditions, when the switch is ON), and at steady-state OFF time (i.e.when the system is up and running, during a potentially unsafecondition, when the switch is OFF).

Reference is now made to FIG. 7A, which illustrates a safety switch 702a comprising an auxiliary power circuit according to illustrativeembodiments. Safety switch 702 a may comprise conductors 708 and 709,transistor Q1, controller 710 and auxiliary power circuit 704. Safetyswitch 702 a may further comprise a communication device similar to orthe same as communication device 305 of FIG. 3 (not explicitly depicted,to reduce visual noise). Transistor Q1 may be similar to or the same astransistor Q1 described with regard to FIG. 3 , resistor R31 may be thesame as R31 of FIG. 3 , diode D31 may be the same as D31 of FIG. 3 ,controller 710 may be similar to or the same as controller 303 of FIG. 3, and conductors 708 and 709 may be similar to or the same as conductors308 and 309, respectively, of FIG. 3 .

Auxiliary power circuit 704 may be coupled in parallel to transistor Q1.A first input of auxiliary power circuit 704 may be coupled to conductor708, and a second input of auxiliary power circuit 704 may be coupled toconductor 709.

In some embodiments, auxiliary power circuit 704 may comprise analogcircuitry configured to provide an appropriate control signal totransistor Q1. In some embodiments, auxiliary power circuit 704 mayprovide power to controller 710, with controller 710 configured toprovide a control signal to transistor Q1.

Reference is now made to FIG. 7B, which illustrates a safety switch 702b comprising an auxiliary power circuit according to illustrativeembodiments. Safety switch 702 b may comprise conductors 708 and 709,transistor Q1, controller 710 and auxiliary power circuit 714. Safetyswitch 702 b may further comprise a communication device similar to orthe same as communication device 305 of FIG. 3 (not explicitly depicted,to reduce visual noise). Transistor Q1 may be similar to or the same astransistor Q1 described with regard to FIG. 3 , resistor R31 may be thesame as R31 of FIG. 3 , diode D31 may be the same as D31 of FIG. 3 ,controller 710 may be similar to or the same as controller 303 of FIG. 3, and conductors 708 and 709 may be similar to or the same as conductors308 and 309, respectively, of FIG. 3 .

Auxiliary power circuit 714 may be coupled in series with transistor Q1.A first input of auxiliary power circuit 714 may be coupled to conductor708, and a second input of auxiliary power circuit 704 a may be coupledto transistor Q1.

Reference is now made to FIG. 7C, which depicts an auxiliary powercircuit according to illustrative embodiments. Auxiliary power circuit704 a may be used as auxiliary power circuit 704 of FIG. 7A. A firstinput to auxiliary power circuit 704 a may be coupled to the sourceterminal of a transistor (e.g. Q1 of FIG. 7A), and a second input toauxiliary power circuit 704 a may be coupled to the drain terminal of atransistor. An output of auxiliary power circuit 704 a may be coupled tothe gate terminal of a transistor. Auxiliary power circuit 704 a maycomprise Ultra Low Voltage Direct-Current to Direct Current (DC/DC)converter (ULVC) 720. Controller 710 may be an analog or digitalcontroller, and may be similar to controller 303 of FIG. 3 . Controller710 may be integrated with or separate from auxiliary power circuit 304a. In some embodiments, an output of ULVC 720 may be coupled to an inputof controller 710, with controller 710 applying a voltage to the gate ofa transistor. ULVC 720 may be configured to receive a very low voltage(e.g. tens or hundreds of millivolts) at its input, and output asubstantially larger voltage (e.g. several volts). ULVC 720 may bevariously implemented. In some embodiments, ULVC may comprise anoscillator charge pump and/or several conversion stages. Variations ofillustrative circuits found in “0.18-V Input Charge Pump with ForwardBody Biasing in Startup Circuit using 65 nm CMOS” (P. H. Chen et. al.,©IEEE 2010), “Low voltage integrated charge pump circuits for energyharvesting applications” (W. P. M. Randhika Pathirana, 2014) may be usedas or as part of ULVC 720.

Reference is now made to FIG. 7D, which shows a timing diagram foroperating auxiliary power circuit 704 a of FIG. 7C according to anillustrative embodiment. As a numerical example, auxiliary power circuit704 a may be coupled as described above to the terminals of a MOSFET.ULVC 720 may be coupled between the source (Vs) and drain (Vd) terminalsof the MOSFET. When the MOSFET is in the OFF position, the voltage dropbetween terminals Vs and Vd may be substantial, e.g. close to theopen-circuit voltage of a PV generator. When the MOSFET is in the OFFposition, ULVC 720 may be bypassed or disabled, with the substantialvoltage drop between terminals Vs and Vd processed to provide power tocontroller 710. Controller 710 may hold the voltage between the MOSFETgate and source terminals to a low value, (e.g. 0V or 1V, under aminimum source-gate threshold of 2V), maintaining the MOSFET in the OFFposition.

Still referring to FIG. 7D, controller 710 may receive a command via acommunication circuit (not explicitly depicted) to turn the MOSFET tothe ON state. Controller 710 may increase the gate-to-source voltage toabout 5V. In illustrative PV systems, the current flowing through a PVstring at certain points of operation may be about 10 A. At agate-to-source voltage of 5V and drain-to-source current of 10 A, thedrain-to-source voltage may be about 90 mV. ULVC 720 may boost thedrain-to-source voltage of 90 mV to a voltage of several volts or more(e.g. 5V, 10V, 12V or 20V) for powering controller 710. Controller 710may continuously hold the gate-to-source voltage at about 5V until acommand is received to turn the MOSFET OFF. In some embodiments, theMOSFET is turned OFF at the end of every day, i.e. when PV generatorscease producing significant power due to nightfall. When it is time toturn the MOSFET OFF, controller may decrease the gate-to-source voltageback to about 0V or 1V.

Operating auxiliary power circuit 704 a according to the illustrativetiming diagrams of FIG. 7D may provide several advantages. For example,the steady-state power consumed by safety switch 702 a using auxiliarypower circuit 704 a may be low, in this illustrative example, 90 mV*10A=900 mW when in the ON position, and 30V*10 uA=0.3 mW when in the OFFposition. Furthermore, the steady-state voltage across safety switch 702a may be substantially constant when in the ON position (e.g. 90 mV).

Reference is now made to FIG. 7E, which depicts an auxiliary powercircuit according to illustrative embodiments. Auxiliary power circuit704 b may be used as auxiliary power circuit 704 of FIG. 7A. A firstinput to auxiliary power circuit 704 b may be coupled to the sourceterminal of a transistor (e.g. Q1 of FIG. 7A), and a second input toauxiliary power circuit 704 b may be coupled to the drain terminal of atransistor. An output of auxiliary power circuit 704 b may be coupled tothe gate terminal of a transistor. Auxiliary power circuit 704 b maycomprise capacitor C2, diode D2, diode Z2, transistor Q70 and DC-to-DCconverter 721. In some embodiments, capacitor C2 may be replaced by adifferent charge device (e.g. a battery). Controller 710 may be analogor digital, and may be similar to controller 303 of FIG. 3 . Controller710 may be integrated with or separate from auxiliary power circuit 304a. Diode Z2 may be a Zener diode designed to limit and hold areverse-bias voltage to a predetermined value. In this illustrativeembodiment, diode Z2 is assumed to have a reverse-bias voltage of 4V. Afirst input to auxiliary power circuit 704 b may be coupled to thesource terminal of a transistor (e.g. Q1 of FIG. 7A), and a second inputto auxiliary power circuit 704 b may be coupled to the drain terminal ofa transistor (e.g. Q1). An output of auxiliary power circuit 704 b maybe coupled to the gate terminal of a transistor (e.g. Q1). In someembodiments, an output of converter 721 may be coupled to an input ofcontroller 710, with controller 710 applying a voltage to the gate of atransistor. Converter 721 may be configured to receive a voltage ofseveral volts (e.g. between 3V-10V) at its input, and output a voltagefor powering controller 710 or controlling the gate voltage of atransistor gate terminal.

The anode of diode D2 may be coupled to a transistor drain terminal(Vd), and the cathode of diode D2 may be coupled to the cathode of diodeZ2 and a first terminal of capacitor C2. The anode of diode Z2 may becoupled to a drain terminal of transistor Q70, with the source terminalof transistor Q70 coupled to a transistor source terminal (Vs) and to asecond terminal of capacitor C2. The gate voltage of transistor Q70 maybe controlled by controller 710 (the control line is not explicitlydepicted). The inputs of converter 721 may be coupled in parallel withcapacitor C2.

Auxiliary power circuits 704 a-b and 714 may be operated to provide avoltage drop across the terminals of safety switch 702 according tosafety and effective system operation requirements. The drain-to-sourcevoltage may be desired to be low during normal system operation, whensafety switch 702 is in the “steady ON state”, i.e. when the switchprovides a low-impedance path for photovoltaic power to flow through aPV string. When safety switch 702 is in a “steady OFF state”, safetyswitch 702 may be required to provide a drain-to-source voltage of aboutan open-circuit voltage of a PV generator without providing alow-impedance path for current flow.

Referring back to FIG. 7E, controller 710 may operate transistor Q70 andtransistor Q1 of FIG. 7A to provide a voltage drop across the terminalsof safety switch 702 according to safety and effective system operationrequirements. In the “steady OFF state”, transistors Q1 and Q70 may beheld in the OFF state. In the “steady ON state” transistor Q1 may be ON,providing a low impedance path between the drain and source terminals,and transistor Q70 may be either ON or OFF. It may be desirable duringthe “steady ON state” to temporarily move Q1 to the “temporarily OFFstate” for a short period of time, to allow capacitor C2 to recharge andcontinue providing operational power to controller 710. In the“temporarily OFF” state, transistor Q1 may be OFF and transistor Q70 maybe ON. Diode Z2 may provide a limited charging voltage (e.g. 4V) acrossthe terminals of capacitor C2, with capacitor C2 providing a currentpath for the current of a PV string.

Reference is now made to FIG. 7F, which shows a timing diagram foroperating auxiliary power circuit 704 b of FIG. 7E according to anillustrative embodiment. As a numerical example, auxiliary power circuit704 a may be coupled as described above to the terminals of a MOSFET.Converter 721 may be coupled between the source (Vs) and drain (Vd)terminals of the MOSFET. When the MOSFET is in the steady-OFF-state, thevoltage drop between terminals Vs and Vd may be substantial, e.g. closeto the open-circuit voltage of a PV generator. When the MOSFET is in thesteady-OFF-state, converter 721 may be bypassed or disabled, with thesubstantial voltage drop between terminals Vs and Vd processed toprovide power to controller 710. In some embodiments, when the MOSFET isin the steady-OFF-state, converter 721 may process the drain-to-sourcevoltage to provide power to controller 710. Controller 710 may hold thevoltage between the MOSFET gate terminal and source terminals to a lowvalue, (e.g. 0V or 1V, under a minimum source-gate threshold of 2V),maintaining the MOSFET in the OFF position. When the MOSFET is in thesteady-OFF-state, capacitor C2 may be charged to about the voltagebetween the drain and source terminals. In some embodiments, diode Z2may be disconnected (e.g. by turning Q70 to the OFF state), to increasethe drain-to-source voltage when the MOSFET is in the steady-OFF-state.In some embodiments, having a large drain-to-source voltage (e.g. aboutthe same voltage as a PV generator open-circuit voltage) when the MOSFETis in the steady-OFF-state increases system safety by decreasing thetotal voltage across a PV generator and an accompanying safety switch.

Still referring to FIG. 7F, controller 710 may receive a command via acommunication circuit (not explicitly depicted) to turn the MOSFET tothe ON state. Controller 710 may increase the gate-to-source voltage ofQ1 to about 6V. In illustrative PV systems, the current flowing througha PV string at certain points of operation may be about 10 A. At agate-to-source voltage of 6V and drain-to-source current of 10 A, thedrain-to-source voltage may be about 65 mV. Diode D2 might not beforward biased (e.g., if diode has a forward voltage of 0.6V, adrain-to-source voltage of 65 mV might not forward-bias diode D2),disconnecting capacitor C2 from the drain terminal. Capacitor C2 mayslowly discharge by providing power to converter 721. Converter 721 mayinclude circuitry (e.g. analog comparators) to monitor the voltageacross capacitor C2, and may respond to the voltage across capacitor C2falling below a first threshold. If the voltage across capacitor fallsbelow the first threshold, controller 710 may reduce the gate-to-sourcevoltage to about 0V or 1V, resulting in the MOSFET moving to the OFFstate. Diode D2 may then become forward-biased, and diode Z2 may limitthe drain-to-source voltage to a second threshold. Transistor Q70 may beheld in the ON state, allowing diode Z2 to regulate the drain-to-sourcevoltage. Capacitor C2 may then be rapidly charged back to about thevoltage level of the second threshold, with controller 710 configured toincrease the gate-to-source voltage back to 6V when capacitor C2 reachesthe second threshold voltage. This iterative process may repeat itselfwhile the MOSFET is operating in a “steady ON state” mode. In theillustrative embodiment illustrated in FIG. 7F, the first threshold is2V, and the second threshold is 4V. The voltage across capacitor C2varies between the two levels, with the gate-to-source voltagealternating between about 0V and about 6V, and the drain-to-sourcevoltage alternating between 4V and 65 mV.

Operating auxiliary power circuit 704 b according to the illustrativetiming diagrams of FIG. 7F may provide several advantages. For example,a converter designed to receive an input voltage between 2-30V (e.g.converter 721) may be cheap, efficient and easy to implement. In someembodiments, additional zener diodes may be coupled in series with diodeZ2, increasing the first voltages. Increasing the first thresholdvoltage (e.g. to 10V, 15V or 20V, respectively) may provide advantagessuch as decreasing the frequency of charge-discharge cycles overcapacitor C2, and may provide a voltage to converter 721 which may beeasier to process.

It is to be understood that illustrative operating points comprisingMOSFET drain-to-source voltages of 65 mV and 90 mV, MOSFETgate-to-source voltages of 5V and 6V, and MOSFET drain-to-sourcecurrents of 10 A are used for illustrative purposes and are not intendedto be limiting of operating points used in conjunction with illustrativeembodiments disclosed herein. In some embodiments, multiple MOSFETtransistors may be parallel-coupled to reduce ON-state resistance,thereby reducing the drain-to-source voltage across MOSFETs when in theON state. For example, coupling five MOSFETs in parallel may reduce adrain-to-source ON-state voltage from 65 mV to 15 mV.

Reference is now made to FIG. 7G, which depicts an auxiliary powercircuit according to illustrative embodiments. Auxiliary power circuit704 c may be used as auxiliary power circuit 704 of FIG. 7A. Auxiliarypower circuit 704 c may be similar to auxiliary power circuit 704 b,with a modification in that the anode of diode Z2 is coupled to thedrain terminal of transistor Q1 (Vs), and that the drain terminal oftransistor Q70 is also coupled to the source terminal of transistor Q1(Vs). When safety switch 702 is in the “steady ON state”, transistors Q1and Q70 may be ON, providing a low impedance path for PV string current.When safety switch 702 is in the “steady OFF state”, transistors Q1 andQ70 may be OFF, preventing a low impedance path for a PV string current,and providing a substantial voltage drop across the terminals of safetyswitch 702 (e.g. about the same voltage or a slightly lower voltage thana PV-generator open-circuit voltage). When safety switch 702 is in the“temporarily OFF state”, transistor Q1 may be OFF and transistor Q70 maybe ON, diode Z2 providing a charging voltage to capacitor C2 and Q70providing a low-impedance current path for a PV string current.

Reference is now made to FIG. 7H, which illustrates a safety switchcomprising an auxiliary power circuit according to illustrativeembodiments. Safety switch 702 c may comprise conductors 708 and 709,transistor Q1, controller 710 and auxiliary power circuit 715. Auxiliarypower circuit 715 may be used auxiliary power circuit 714 of FIG. 7B. Inthis illustrative embodiment, auxiliary power circuit 715 may double asa power line communication (PLC) device. Inductor L4, capacitor C3 andresistor R may be coupled in parallel, with a first node of inductor L4coupled to conductor 708, and a second node of inductor L4 coupled tothe source terminal of transistor Q1. The values of inductor L4 andcapacitor C3 may be selected to resonate at a resonant frequency (e.g.60 kHz).

Still referring to FIG. 7H, an external device (e.g. system power device110 of FIG. 1 ) may transmit a PLC high-frequency alternating currentsignal (e.g. using frequency shift keying, amplitude modulation or othermodulation schemes) over conductor 708. The PLC signal may induce ahigh-frequency alternating-current voltage drop across the terminals ofresistor R, with diode D7 providing a voltage to controller 710 when thevoltage across resistor R is positive (i.e. the voltage at conductor 708is higher than the voltage at the source terminal of transistor Q1). Insome embodiments, diode D7 may be replaced by a “full bridge” of diodesproviding a voltage to controller 710 when the voltage across R isnonzero (either positive or negative). In some embodiments, thePLC-induced voltage across resistor R may serve a dual purpose. The PLCsignal may provide operational information to controller 710 by varyingthe voltage drop across resistor R. Additionally, in some embodiments,the PLC signal may provide operational power to controller 710.Controller 710 may draw power from the resonant circuit comprisingresistor R, capacitor C3 and inductor L4, and use the drawn power to setthe state of transistor Q1.

Implementing auxiliary power circuit 715 as illustrated in FIG. 7H mayprovide certain advantages. For example, auxiliary power circuit 715 ofFIG. 7H may double as a communication device, reducing the totalcomponent count in safety switch 702 c. Furthermore, integrating controland power signals may reduce the complexity required to programcontroller 710. For example, an ‘ON’ signal may be broadcast by a systemcontroller at a high power, and an ‘OFF’ signal may be broadcast by asystem controller at low power. Auxiliary power circuit 715 may directlyapply the converted power signal to the gate of transistor Q1, whereinthe power of the ‘ON’ signal may be sufficient to hold Q1 in the ONstate, and the power of the ‘OFF’ signal might not be sufficient to holdQ1 in the ON state.

Elements of auxiliary power circuits 704 a, 704 b and 715 may bevariously combined. For example, auxiliary power circuit 714 of FIG. 7Bmay be added to safety switch 702 a of FIG. 7A, auxiliary power circuit714 functioning as a PLC circuit as well as being configured to providepower to controller 710 in case of a malfunction in auxiliary powercircuit 704. In some embodiments, auxiliary power circuit 714 mayprovide initial power to controller 710 at system setup, with auxiliarypower circuit 704 providing power to controller 710 during “steadystate” operation.

Reference is now made to FIG. 7I, which illustrates part of a MOSFETdatasheet according to an illustrative embodiment. Plot 770 may depictrelationships between drain-to-source voltage and drain-to-sourcecurrent through a MOSFET. Curve 771 may depict a current-voltagerelationship when the gate-to-source voltage applied to a MOSFET is 5V.Curve 771 may depict a current-voltage relationship when thegate-to-source voltage applied to a MOSFET is 6V. Operating point A mayindicate that when a gate-to-source voltage applied to a MOSFET is 6Vand the drain-to-source current flowing through the MOSFET is 10 A, thedrain-to-source voltage across the MOSFET is about 65 mV. This maycorrespond to a possible operating point for a MOSFET operated accordingto FIG. 7F. Operating point B may indicate that when a gate-to-sourcevoltage applied to a MOSFET is 5V and the drain-to-source currentflowing through the MOSFET is 10 A, the drain-to-source voltage acrossthe MOSFET is about 90 mV. This may correspond to a possible operatingpoint for a MOSFET operated according to FIG. 7D. As noted above, theseoperating points are illustrative only, and may adapted by connectedmultiple MOSFETs in parallel to obtain new operating points.

Reference is now made to FIG. 8 , which shows a photovoltaic (PV) systemaccording to illustrative embodiments. PV system 800 may comprise aplurality of PV strings 804 coupled in parallel between a ground bus anda power bus. Each of PV strings 804 may comprise a plurality ofphotovoltaic generators 801, a plurality of safety switches 802 and aplurality of PV power devices 803. PV generators 801 may be similar toor the same as PV generators 101 of FIG. 1A, and safety switches 802 maybe similar to or the same as safety switch 102 of FIG. 1A, safety switch302 of FIG. 3 and/or safety switches 702 a-702 c of FIGS. 7A-7C.

In some embodiments, the power and ground buses may be input to systempower device 810. In some embodiments, system power device 810 mayinclude a DC/AC inverter and may output alternating current (AC) powerto a power grid, home or other destinations. In some embodiments, systempower device 810 may comprise a combiner box, transformer and/or safetydisconnect circuit. For example, system power device 810 may comprise aDC combiner box for receiving DC power from a plurality of PV strings804 and outputting the combined DC power. In some embodiments, systempower device 810 may include a fuse coupled to each PV string 804 forovercurrent protection, and/or one or more disconnect switches fordisconnecting one or more PV strings 804. In some embodiments, systempower device 810 may comprise a system controller (e.g. a Digital SignalProcessor (DSP), Application-Specific Integrated Circuit (ASIC) and/or aField Programmable Gate Array (FPGA)) for providing commands to andreceiving data from PV power devices 803 and safety switches 802.

Each safety switch 802 may be coupled between a first output of a firstPV generator and a second output of a second output generator, and eachPV power device may have two input terminals: a first input terminalcoupled to the second output of the first PV generator, and a secondinput terminal coupled to the first output of the second PV generator.In this “two-to-one” arrangement, each pair of PV generators 801 areeffectively coupled in series, with the combined voltage and power ofthe two PV generators provided to the input of PV power device 803. Eachsafety switch 802 is disposed between the two PV generators, fordisconnecting the pair of PV generators in case of a potentially unsafecondition.

Some conventional PV installations feature a similar arrangement, witheach pair of PV generators 801 directly connected to each other withouta safety switch disposed in between the generators. In case of an unsafecondition, a PV power device 803 may stop drawing power from the PVgenerators, resulting in an open-circuit voltage at the PV power deviceinput terminals which is about double the open-circuit voltage of eachPV power generator. This voltage may, in some systems, be as high as 80,100 or even 120 volts, which may be higher than the allowed safe voltagedefined by safety regulations.

By operating safety switches 802 according to apparatuses and methodsdisclosed herein, in case of an unsafe condition (e.g. detected bysystem power device 810, a PV power device 803 and/or a safety switch802), one or more safety switches 802 may move to the OFF state,reducing the voltage drop between the input terminals of each PV powerdevice 803 to about 40-60 volts, which may be an adequately safe voltagelevel.

Each PV power device 803 may receive power from two photovoltaicgenerators 801 coupled to the inputs of PV power device 803, and mayprovide the combined power of the two photovoltaic generators at theoutputs of PV power device 803. The outputs of a plurality of PV powerdevices 803 may be coupled in series to form a PV string 804, with aplurality of PV strings 804 coupled in parallel to provide power tosystem power device 810.

While FIG. 8 illustrates an arrangement wherein two PV generators 801are coupled in parallel to each PV power device 803, variousarrangements can be easily obtained. For example, each PV power devicereceive power from three or more serially-connected PV generators 801,with safety switches 802 disposed between the PV generators. In someembodiments, some PV power devices 803 may receive power from a singlePV generator 801, some PV power devices may receive power from two PVgenerators 801, and some PV power devices may receive power from morethan two PV generators 801. In some embodiments, PV power devices 803may receive power from multiple parallel-connected serial strings of PVgenerators 801, with safety switches 802 disposed in the serial strings.Embodiments disclosed herein include the aforementioned modifications,and other modifications which will be evident to one of ordinary skillin the art.

Reference is now made to FIG. 9 , which illustrates circuitry which maybe found in a power device such as power device 903, according to anillustrative embodiment. PV power device 903 may be similar to or thesame as PV power device 803 of FIG. 8 . In some embodiments, PV powerdevice 903 may include power converter 900. Power converter 900 maycomprise a direct current-direct current (DC/DC) converter such as aBuck, Boost, Buck/Boost, Buck+Boost, Cuk, Flyback and/or forwardconverter. In some embodiments, power converter 900 may comprise adirect current-alternating current (DC/AC) converter (also known as aninverter), such a micro-inverter. Power converter 900 may have two inputterminals and two output terminals, which may be the same as the inputterminals and output terminals of PV power device 903. In someembodiments, PV power device 903 may include Maximum Power PointTracking (MPPT) circuit 906, configured to extract increased power froma power source the power device is coupled to. In some embodiments,power converter 900 may include MPPT functionality. In some embodiments,MPPT circuit 906 may implement impedance matching algorithms to extractincreased power from a power source the power device is coupled to Powerdevice 903 may further comprise controller 905 such as a microprocessor,Digital Signal Processor (DSP), Application-Specific Integrated Circuit(ASIC) and/or a Field Programmable Gate Array (FPGA).

Still referring to FIG. 9 , controller 905 may control and/orcommunicate with other elements of power device 903 over common bus 920.In some embodiments, power device 903 may include circuitry and/orsensors/sensor interfaces 904 configured to measure parameters directlyor receive measured parameters from connected sensors and/or sensorinterfaces 904 configured to measure parameters on or near the powersource, such as the voltage and/or current output by the power sourceand/or the power output by the power source. In some embodiments thepower source may be a PV generator comprising PV cells, and a sensor orsensor interface may directly measure or receive measurements of theirradiance received by the PV cells, and/or the temperature on or nearthe PV generator.

Still referring to FIG. 9 , in some embodiments, power device 903 mayinclude communication device 911, configured to transmit and/or receivedata and/or commands from other devices. Communication device 911 maycommunicate using Power Line Communication (PLC) technology, or wirelesstechnologies such as ZigBee™, Wi-Fi, cellular communication or otherwireless methods. In some embodiments, power device 903 may includememory device 909, for logging measurements taken by sensor(s)/sensorinterfaces 904 to store code, operational protocols or other operatinginformation. Memory device 909 may be flash, Electrically ErasableProgrammable Read-Only Memory (EEPROM), Random Access Memory (RAM),Solid State Devices (SSD) or other types of appropriate memory devices.

Still referring to FIG. 9 , in some embodiments, PV power device 903 mayinclude safety devices 907 (e.g. fuses, circuit breakers and ResidualCurrent Detectors). Safety devices 907 may be passive or active. Forexample, safety devices 907 may comprise one or more passive fusesdisposed within power device 903 and designed to melt when a certaincurrent flows through it, disconnecting part of power device 903 toavoid damage. In some embodiments, safety devices 907 may compriseactive disconnect switches, configured to receive commands from acontroller (e.g. controller 905, or an external controller) todisconnect portions of power device 903, or configured to disconnectportions of power device 903 in response to a measurement measured by asensor (e.g. a measurement measured or obtained by sensors/sensorinterfaces 904). In some embodiments, power device 903 may compriseauxiliary power circuit 908, configured to receive power from a powersource coupled to power device 903, and output power suitable foroperating other circuitry components (e.g. controller 905, communicationdevice 911, etc.). Communication, electrical coupling and/ordata-sharing between the various components of power device 903 may becarried out over common bus 920.

Still referring to FIG. 9 , in some embodiments, PV power device 903 maycomprise transistor Q9 coupled between the inputs of power converter900. Transistor Q9 may be controlled by controller 905. If an unsafecondition is detected, controller 905 may set transistor Q9 to ON,short-circuiting the input to power converter 900. Transistor Q9 may becontrolled in conjunction with safety switch 802 of FIG. 8 . When safetyswitch 802 and transistor Q9 are OFF, each pair of PV generators 801 ofFIG. 8 are disconnected, each PV generator providing an open-circuitvoltage at its output terminals. When safety switch 802 and transistorQ9 are ON, each pair of PV generators 801 of FIG. 8 are connected andshort-circuited, the pair of PV generators providing a voltage of aboutzero to power converter 900. In both scenarios, a safe voltage at allsystem locations may be maintained, and the two scenarios may bestaggered to alternate between open-circuiting and short-circuiting PVgenerators. This mode of operation may allow continuous power supply tosystem control devices, as well as provide backup mechanisms formaintaining a safe voltage (i.e. in case a safety switch 802malfunctions, operation of transistor Q9 may allow continued safeoperating conditions).

Reference is now made to FIG. 10 , which shows a photovoltaic (PV)system according to illustrative embodiments. PV system 1000 maycomprise a plurality of PV strings 1004 coupled in parallel between aground bus and a power bus. Each of PV strings 1004 may comprise aplurality of photovoltaic generators 1001 and a plurality of PV powerdevices 1003. PV generators 1001 may be similar to or the same as PVgenerators 801 of FIG. 8 . In some embodiments, the power and groundbuses may be input to system power device 1010, which may be similar toor the same as system power device 810 of FIG. 8 .

Each of photovoltaic power devices 1003 may comprise four inputterminals: T1, T2, T3 and T4. T1 and T2 may be coupled to and receivepower from a first PV generator, and T3 and T4 may be coupled to andreceive power from a second PV generator. In some embodiments, PV powerdevice 1003 may be substantially the same as PV power device 803 of FIG.8 , with the addition of safety switch 802 integrated into PV powerdevice 1003 and connected in between terminals T2 and T3 of PV powerdevice 1003.

Reference is now made to FIG. 11A, which shows a photovoltaic powerdevice according to illustrative embodiments. PV power device 1103 a maybe used as PV power device 1003 of FIG. 10 . PV power device 1103 a maycomprise a PV power device similar to or the same as PV power device 803of FIG. 8 or PV power device 903 of FIG. 9 . For convenience, in theillustrative embodiments of FIG. 11A and FIG. 11B, PV power device 1103a will be assumed to comprise PV power device 903 of FIG. 9 .

PV power device 1103 a may comprise transistors Q3, Q4 and Q5.Transistors Q3-Q5 may be MOSFETs, JFETs, IGBTs, BJTs or otherappropriate transistors. For the illustrative embodiment of FIG. 11A,transistors Q3-Q5 will be assumed to be MOSFETs. Transistor Q3 may beconnected between input terminals T2 and T3. Transistor Q4 may beconnected between input terminals T2 and T4. Transistor Q1 may beconnected between input terminals T1 and T3. Transistors Q3-Q5 may becontrolled (e.g. have gate signals provided) by one or more controllerssuch as controller 905 of PV power device 903. The elements comprisingPV power device 1103 a may be jointly enclosed by enclosure 1108.

A first PV generator (not explicitly depicted) may be coupled betweenterminals T1 and T2, and a second PV generator (not explicitly depicted)may be coupled between terminals T3 and T4. Under normal operatingconditions, transistor Q3 may be ON, and transistors Q4 and Q5 may beOFF. Under these conditions, the two photovoltaic generators may beserially connected, with the combined serial voltage of the two PVgenerators provided between terminals T1 and T4. When a potentiallyunsafe condition is detected, the controller controlling transistor Q3may turn Q3 to the OFF state, reducing the voltage drop betweenterminals T1 and T4.

Even when transistor Q3 is OFF, power may still be provided at the inputto PV power device 903. For example, in some embodiments, controller(s)controlling transistors Q4 and Q5 may switch Q4 and Q5 to the ON statewhen Q3 is OFF, resulting in terminal T1 being short-circuited toterminal T3, and terminal T2 being short-circuited to terminal T4. Underthese conditions, the first and second photovoltaic generator may becoupled in parallel between terminal T1 and T4, allowing PV power device903 to draw power from the PV generators (e.g. for powering devices suchas controller 905, communication device 911, auxiliary power circuit 908and other devices depicted in FIG. 9 ). In some embodiments, Q4 or Q5might not be included in PV power device 1103 a. For example, Q4 mightnot be included, in which case by turning Q5 to the ON position when Q3is OFF, power is provided to PV power device 903 by a single PVgenerator (coupled between T3 and T4). Similarly, Q5 might not beincluded, in which case by turning Q4 to the ON position when Q3 is OFF,power is provided to PV power device 903 by a single PV generator(coupled between T1 and T2).

Reference is now made to FIG. 11B, which shows a photovoltaic powerdevice according to illustrative embodiments. PV power device 1103 b maybe used as PV power device 1003 of FIG. 10 . PV power device 1103 b maycomprise a PV power device similar to or the same as PV power device 803of FIG. 8 or PV power device 903 of FIG. 9 . For convenience, in theillustrative embodiments of FIG. 11A and FIG. 11B, PV power device 1103a will be assumed to comprise PV power device 903 of FIG. 9 .

Transistor Q6 may be similar to or the same as transistor Q3 of FIG.11A. PV power device 1103 b may further comprise diodes D3 and D4. Theanode of diode D3 may be coupled to terminal T3 and the cathode of diodeD3 may be coupled to the positive input of PV power device 903 at nodeN1. The anode of diode D4 may be coupled to terminal T1 and the cathodeof diode D3 may be coupled to the positive input of PV power device 903at node N1. The elements comprising PV power device 1103 b may bejointly enclosed by enclosure 1108.

Still referring to FIG. 11B, a first PV generator (not explicitlydepicted) may be coupled between terminals T1 and T2, and a second PVgenerator (not explicitly depicted) may be coupled between terminals T3and T4. Under normal operating conditions, transistor Q3 may be ON,connecting terminals T2 and T3. The voltage at terminal T1 may be higherthan the voltage at terminal T2 (e.g. if the positive output of a PVgenerator is coupled to terminal T1 and the negative output of the PVgenerator is coupled to terminal T2), so diode D4 may be forward-biasedand diode D3 may be reverse-biased. The voltage at node N1 may be aboutthe voltage at terminal T1 (assuming an insignificant voltage dropacross diode D4), resulting in a voltage input to PV power device 903about equal to the voltage between terminals T1 and T4.

When a potentially unsafe condition is detected, the controllercontrolling transistor Q6 may turn Q6 to the OFF state, disconnectingthe coupling of terminals T2 and T3. The voltage at node N1 may be thevoltage at terminal T1 or the voltage at terminal T3, the greater of thetwo. While the voltage at node N1 might not be predetermined, in eitherpossible scenario, a PV generator may be coupled to the inputs of PVpower device 903, providing power to PV power device 903 (e.g. forpowering devices such as controller 905, communication device 911,auxiliary power circuit 908 and other devices depicted in FIG. 9 ).

Reference is now made to FIG. 12 , which shows a photovoltaic (PV)system according to illustrative embodiments. PV system 1200 maycomprise a plurality of PV strings 1204 coupled in parallel between aground bus and a power bus. Each of PV strings 1204 may comprise aplurality of photovoltaic generators 1201, a plurality of safetyswitches 1202 and a plurality of PV power devices 1203. PV generators1001 may be similar to or the same as PV generators 801 of FIG. 8 . Insome embodiments, the power and ground buses may be input to systempower device 1210, which may be similar to or the same as system powerdevice 810 of FIG. 8 .

Each PV power device 1203 may be designed to be coupled to more than onePV power generator 1201. For example, in PV system 1200, each PV powerdevice 1203 (except for the PV power devices coupled to the power bus)is coupled to two PV power generators and to two safety switches 1202,with each safety switch 1202 (except for the safety switch 1202 which iscoupled to the ground bus) coupled to two PV generators 1201 and two PVpower devices 1203.

Under normal operating conditions, each PV power device 1203 may receivepower from two PV generators 1201, and may forward the power along PVstring 1204 towards the power bus. Under normal operating conditions,each safety switch 1202 may provide a connection between two PVgenerators 1201 and may provide a connection between two PV powerdevices 1203 for forwarding power along PV string 1204. For example,under normal operating conditions, safety switch 1202 a provides aconnection between PV generators 1201 a and 1201 b. PV power device 1203a may receive power generated by PV generators 1201 a and 1201 b, withsafety switches 1202 b disposed between PV power devices 1203 a and 1203b, providing PV power device 1203 a with a connection for forwardingpower to PV power device 1203 b. Similarly, safety switch 1202 bprovides a connection between PV generators 1201 c and 1201 d, with PVpower device 1203 b receiving power from PV generators 1201 c and 1201d.

In case of an unsafe condition, safety switch 1202 a may be operated todisconnect PV generator 1201 a from PV generator 1201 b, and todisconnect PV power device 1203 a from the ground bus. Similarly, safetyswitch 1202 b may be operated to disconnect PV generator 1201 c from PVgenerator 1201 d, and to disconnect PV power device 1203 a PV powerdevice 1203 b. Operating safety switches 1202 in this manner may reducethe voltage in various locations in PV system 1200 to safe voltagelevels.

Reference is now made to FIG. 13A, which shows safety switch 1205according to an illustrative embodiment. Safety switch 1205 may compriseterminals T1-T4, transistors (e.g. MOSFETs) Q7 and Q8, capacitors C4 andC5, and inductors L4 and L5. Inductor L4 may be provided betweenterminal T3 and terminal T1 to reduce ripples and/or spikes in a currentflowing from terminal T1 to terminal T3, and inductor L5 may be providedbetween terminal T4 and midpoint node X to reduce ripples and/or spikesin a current flowing from transistor Q7 to terminal T4. In someembodiments, inductors L4 and L5 might not be provided. In someembodiments, transistors Q7 and Q8 may be replaced by alternativeswitching elements, such as IGBTs, BJTs, JFETs or other switchingelements. Capacitor C4 may be coupled between terminals T1 and T2.Transistor Q7 may be coupled between terminal T2 and midpoint node X,and capacitor C5 may be coupled between terminal T1 and midpoint node X.Transistor Q8 may be coupled in parallel to capacitor C5, betweenterminal T1 and midpoint node X. In some embodiments, capacitor C5and/or capacitor C4 might not be provided.

During normal system operation, transistor Q7 may be held in the ONstate, and transistor Q8 may be in the OFF state. Capacitor C5 may thenbe in parallel with capacitor C4, and a first PV generator may becoupled between terminals T1 and T2, applying a voltage to capacitors C4and C5 and providing electrical power at terminals T1 and T2. TerminalT4 may be coupled to an output terminal of a second PV generator, andterminal T3 may be coupled to an input terminal of a PV power device1203. The power input to safety switch 1205 at terminals T1 and T2 maybe output at terminals T3 and T4 to the second PV generators and the PVpower device 1203.

Transistors Q7 and Q8 may be controlled by a controller (not explicitlydepicted) similar to or the same as controller 710 of FIG. 7A. In someembodiments, the controller may be powered by capacitor C4 (e.g. acontroller input power terminal may be coupled to terminal T2 orterminal T1 for receiving power from capacitor C4). Safety switch 1205may further comprise a communication device (e.g. similar to or the sameas communication device 305 of FIG. 3 ) for receiving operationalcommands from a system control device.

When an unsafe condition is detected, the controller may switchtransistor Q7 to the OFF state and transistor Q8 to the ON state.Capacitor C5 may be short-circuited by transistor Q8, while capacitor C4may maintain the voltage imposed between terminals T1 and T2.

Reference is now made to FIG. 13B, which shows some of the internalcircuitry of a photovoltaic power device according to one illustrativeembodiment. In some embodiments, PV power device 1203 may comprise avariation of a Buck+Boost DC/DC converter. The power device may includea circuit having two input terminals, denoted Vin and common, and twooutput terminals which output the same voltage Vout. The output voltageis in relation to the common terminal. The circuit may include an inputcapacitor Cin coupled between the common terminal and the Vin terminal,an output capacitor coupled between the common terminal and the Voutterminals. The circuit may include two central points used forreference. The circuit may include a plurality of switches (e.g. MOSFETtransistors) Q11, Q12, Q13 and Q14 with Q11 connected between Vin andthe first central point, and Q12 connected between the common terminaland the first central point. Q13 may be connected between the Voutterminal and the second central point, and Q14 may be connected betweenthe common terminal and the second central point. The circuit mayfurther include inductor L6 coupled between the two central points.

The operation of the Buck+Boost DC/DC converter in PV power device 1203may be variously configured. If an output voltage lower than he inputvoltage is desired, Q13 may be statically ON, Q14 may be statically OFF,and with Q11 and Q12 being Pulse-Width-Modulation (PWM)-switched in acomplementary manner to one another, the circuit is temporarilyequivalent to a Buck converter and the input voltage is bucked. If anoutput voltage higher than he input voltage is desired, Q11 may bestatically ON, Q12 may be statically OFF, and with Q13 and Q14 beingPWM-switched in a complementary manner to one another, the input voltageis boosted. Staggering the switching of switches Q11 and Q12, thecircuit may convert the input voltage Vin to output voltage Vout. Ifcurrent is input to the circuit by the Vin and common terminals, and thevoltage drop across capacitors Cin and Cout are about constant voltagesVin and Vout respectively, the currents input to the circuit arecombined at inductor L6 to form an inductor current which is equal tothe sum of the current input at the Vin and common terminals. Theinductor current may contain a ripple due to the charging anddischarging of capacitors Cin and Cout, but if the voltage drop acrosscapacitors Cin and Cout are about constant, the voltage ripples over thecapacitors are small, and similarly the inductor current ripple may besmall. The inductor current may be output by the pair of outputterminals Vout. In some embodiments, a single output terminal may beincluded, and system designers may split the output terminal externally(i.e. outside of the PV power device circuit), if desired.

In illustrative embodiments, PV power device 1203 may be similar to orthe same as PV power device 903 of FIG. 9 , with power converter 900 ofFIG. 9 comprising the Buck+Boost converter of FIG. 13B. In someembodiments, boosting the voltage input to a PV power device 1203 mightnot be necessary, in which case PV power device 1203 may comprise a Buckconverter similar to the Buck+Boost converter of FIG. 13B, with switchQ14 removed (i.e. replaced by an open-circuit) and switch Q13 replacedwith a wire (i.e. connecting the Vout terminal to the second centralpoint).

Referring back to FIG. 12 , safety switch 1202 b may be coupled tophotovoltaic generators 1201 c and 1201 d, and to PV power devices 1203a and 1203 b. Terminal T2 may be connected to the positive output of PVgenerator 1201 c, and terminal T4 may be connected to the negativeoutput of PV generator 1201 d. Terminal T1 may be coupled to a firstVout terminal of PV power device 1203 a, and terminal T3 may be coupledto the common terminal of PV power device 1203 b. The positive outputterminal of PV generator 1201 d may be coupled to the Vin terminal of PVpower device 1203 b, and the negative output terminal of PV generator1201 c may be coupled to a second Vout terminal of PV power device 1203a. Under normal operating conditions, PV generators 1201 c and 1201 dare serially coupled, the combined voltage of PV generators 1201 c and1201 d input between the common and Vin terminals of PV power device1203 b. If an unsafe condition is detected, safety switch 1202 b maydisconnect the connection between terminals T2 and T4 (e.g. by settingtransistor Q7 of FIG. 13A to OFF) and couple terminals T3 and T4 (e.g.by setting transistor Q8 of FIG. 13A to ON). As a result, PV generator1201 d may be coupled between the common and Vin terminals of PV powerdevice 1203 b, and PV generator 1201 c may be coupled between terminalsT1 and T2 of safety switch 1202 b.

The system topology illustrated in FIG. 12 may provide certainadvantages. For example, during normal system operation, two PVgenerators 1201 provide a combined voltage and power to a PV powerdevice 1203, requiring a reduced number of PV power devices forprocessing power generated by the PV generators. Furthermore, continuousoperational power (i.e. power used for powering device components suchas controllers and transistors) is provided to all PV power devices 1203and safety switches 1202 both during normal operations and during apotentially unsafe condition.

Reference is now made to FIG. 14 , which shows part of a chain ofphotovoltaic devices according to an illustrative embodiment. Chain 1400may comprise a plurality of PV power devices 1203 and a plurality ofsafety switches 1202. Each safety switch 1202 may be connected, usingconductors, between two PV power devices 1203. Terminal T1 of safetyswitch 1202 may be connected to a Vout terminal of a first PV powerdevice, and terminal T3 of safety switch 1202 may be connected to acommon terminal of a second PV power device. Terminals T2 and T4 may beaccessible via external connectors similar to or the same as connectors406 and 407 of FIG. 4A. Similarly, a Vout terminal and a Vin terminal ofeach PV power device 1203 may be accessible via external connectorssimilar to or the same as connectors 406 and 407 of FIG. 4A. Conductorsconnecting a PV power device terminal (e.g. the common terminal) to asafety switch terminal (e.g. terminal T3) may be sized to facilitateconnecting chain 1400 to a plurality of PV generators, as depicted inFIG. 12 . For example, in locales where PV generators are commonly 1-2meters wide, each conductor disposed between a safety switch 1202 and aPV power device 1203 may be about 1-2 meters long. Chain 1400 may beassembled and sold as a single unit, saving cost and time whenconstructing a PV installation similar to or the same as PV system 1200of FIG. 12 .

Referring to FIG. 15 , an illustrative application running on a smartphone, tablet, computer, workstation, mobile device (such as a cellulardevice) and/or a similar computing device is shown. The application mayprovide a list of safety switches disposed in an electrical power system(e.g. system 100 of FIG. 1 ). The application may indicate a serialnumber or other identifying information of each safety switch, as wellas identifying information of coupled PV generators and/or identifyinginformation of a PV string each safety switch is coupled to. In someembodiments, the application may indicate the state of each safetyswitch and/or electrical parameters of one or more safety switches, forexample, the voltage across or current through one or more safetyswitches. In some embodiments, the application may provide touch-screenbuttons or similar input controllers for controlling the state of one ormore switches. For example, activating a button 151 may move anassociated safety switch to the OFF state, and activating a button 152may move an associated safety switch to the ON state. Activating button153 may move all safety switches to the OFF state, and activating button154 may move all safety switches to the ON state. In some embodiments,activating buttons 151-154 may be restricted based on a user accesslevel. For example, the application may enable buttons 151-154 only whenrunning in “Installer/Administrator” mode, to restrict the actions ofunsophisticated users.

Still referring to FIG. 15 , activating button 155 may enable a user toreconfigure a threshold. For example, an electrical voltage, current orpower threshold which may be indicative of an arcing condition andtrigger a system response (e.g. moving one or more safety switches tothe OFF state) may be reconfigured by a user using the application ofFIG. 15 . Activating button 156 may display a graphical layout of anelectrical system represented by the application, including physicallocation details of one or more safety switches. Activating button 157may download current or past operational system data such as the stateof safety switches, and/or electrical parameter measurement measured bysafety switches. Buttons 155-157 may similarly be restricted dependingon the level of user authorization.

The application of FIG. 15 may communicate directly with safety switchesvia wireless communications (e.g. cellular communication, or over theinternet). In some embodiments, the application may communicate with asystem power device (e.g. system power device 110 of FIG. 1 ), with thesystem power device configured to relay communication between theapplication and the safety switches via wireless communication or wiredcommunication (e.g. power line communication).

Reference is now made to FIG. 16 , which illustrates another aspect ofthe present disclosure. A PV power device 1603 may be similar to or thesame as PV power device 903 of FIG. 9 , and correspondingly, PV powerdevice 803 of FIG. 8 . Components depicted and described above withreference to FIG. 9 are correspondingly depicted in FIG. 16 . Hence,power converter 1600 may be analogous to power converter 900 of FIG. 9 .Likewise, sensor(s) 1604 may be analogous to sensor(s) 904 of FIG. 9 ;controller 1605 may be analogous to controller 905 of FIG. 9 ; and soforth for the other components of the PV power device 903, such asMaximum Power Point Tracking (MPPT) circuit 1606; safety devices 1607;auxiliary power circuit 1608; memory device 1609; communication device1611; and common bus 1620, and so forth.

According to some aspects of the disclosure, PV power device 1603 mayinclude power converter 1600 similar to, for example, PV power converter900. Power converter 1600 may comprise a direct current-direct current(DC/DC) converter such as a Buck, Boost, Buck/Boost, Buck+Boost, Cuk,Flyback and/or forward converter. According to some aspects, powerconverter 1600 may comprise a direct current-alternating current (DC/AC)converter (also known as an inverter), such a micro-inverter. PV powerdevice 1603 may have three input terminals, T_(in1), T_(in2), andT_(in3), and two output terminals (not labelled, for clarity ofdepiction).

Still referring to FIG. 16 , according to some aspects of thedisclosure, PV power device 1603 may comprise switch S16, which may becoupled between input terminals T_(in1), T_(in2). Photovoltaic generator1601 a may comprise an output terminal connected to an input terminal ofPV power device 1603, for instance, to input terminal T_(in1).Photovoltaic generator 1601 a may also comprise a second output terminalwhich may be connected to a negative output terminal of photovoltaicgenerator 1601 b. The output from photovoltaic generator 1601 a to thenegative output terminal of photovoltaic generator 1601 b may alsoconnect to PV power device 1603 at input terminal T_(in2). Theconnection to both the negative output terminal of photovoltaicgenerator 1601 b and to an input terminal of PV power device 1603 may bevia, for example, T-connector 1631. T-connector 1631 may, over inputterminal T_(in2), connect to PV power device 1603. Terminal T_(in2) mayterminate at a switch S16, which is comprised in PV power device 1603.Switch S16 may comprise a transistor, similar to transistor Q9 of FIG. 9. Alternatively, the switch S16 may comprise a relay or a different typeof switch (e.g. an IGBT, BJT and the like). Photovoltaic generator 1601b may comprise an output terminal connected to an input terminal of PVpower device 1603 via terminal T_(in3).

Switch S16 may comprise a control terminal. The control terminal ofswitch S16 may be controlled by controller 1605. Correspondingly,controller 1605 may be configured to control switch S16. If an unsafecondition, such as a grid-outage, overvoltage, undervoltage, a problemwith the inverter (such as, but not limited to, the inverter describedabove with reference to power converter 900), or any other problem whichmay result in a potentially unsafe condition, or a failure in thephotovoltaic generator 1601 a, is detected, controller 1605 may turn onswitch S16, short-circuiting the input terminals of photovoltaicgenerator 1601 a in order to protect, reduce the risk for, and so forth,power converter 1600 and/or personnel in the physical proximity of PVpower device 1603. When switch S16 is OFF, the two PV generators 1601 aand 1601 b may be connected in series and to the input terminals ofpower converter 1600. In both scenarios, a safe voltage at locationswithin the system may be maintained. When switch S16 is ON, PV generator1601 a is short-circuited, and a reduced voltage between terminalsT_(in3) and T_(in1) is obtained. Switch S16 being OFF may be indicativeof normal operating conditions, and under normal operating conditions anincreased voltage between terminals T_(in3) and T_(in1) may bepermissible.

In an example of an aspect of system operation, communication device1611 may enable sensor(s) 1604 to monitor the system described hereinacross above the common bus 1620 for a “keep alive” signal, as describedabove with reference to FIG. 6 . In the absence of said “keep alive”signal, sensor(s) 1604 signals controller 1605 that a potentially unsafecondition might be occurring. Controller 1605 then may actuate switchS16 (which may comprise a transistor, for instance, as already noted) inorder to short circuit PV generator 1601 a. Upon receipt of a wakeup or“keep alive” signal, in the event that switch S16 is ON, the controllermay eliminate the short circuit across PV generator 1601 a by turningswitch S16 OFF.

It is appreciated that in the aspect of the present disclosure describedherein above, in the event that PV generator 1601 a fails, PV powerdevice 1603 may continue working as long as switch S16 is turned ON. Insuch a case, PV power device 1603 may continue to receive power from PVgenerator 1601 b. It is also appreciated that T-connector 1631 mayprovide a test point for measuring voltage across the PV generator 1601a, thereby enabling calculation of the individual operating parametersof each of PV generator 1601 a and PV generator 1601 b. Voltmeter 1642is depicted in FIG. 16 in parallel to switch S16 to indicate thisaspect.

According to another aspect of the present disclosure, an additionalswitch (not depicted) might be positioned between terminals, T_(in2) andT_(in3). The additional switch may also be controlled by controller1605. In such an aspect, when both the additional switch is OFF, andswitch S16 is OFF, the two PV generators 1601 a and 1601 b are connectedin series to input terminals of power converter 1600. When switch S16 isON, and the additional switch is OFF, the output terminals ofphotovoltaic generator 1601 a are short circuited and photovoltaicgenerator 1601 b provides the power to the input terminals to powerconverter 1600. Correspondingly, when the additional switch is ON andswitch S16 is OFF, the output terminals of photovoltaic generator 1601 bare short circuited and photovoltaic generator 1601 a provides the powerto the input terminals of power converter 1600. The ability to shortcircuit either one of photovoltaic generator 1601 a or photovoltaicgenerator 1601 b may make the system failure proof for each of the twophotovoltaic generators 1601 a and 1601 b. When both switch S16 is ON,and the additional switch is ON, the output terminals of both PVgenerators 1601 a and 1601 b are short-circuited, thereby the inputterminals of power converter 1600 are also short-circuited. Switch S16(as noted above) and the additional switch may comprise a relay, atransistor, including, but not limited to a MOSFET, an IGBT, a BJT, aJFET, and so forth, or another appropriate switching element.

In still another aspect of the present disclosure, a single photovoltaicgenerator (not depicted) may be utilized rather than photovoltaicgenerator 1601 a and photovoltaic generator 1601 b. The singlephotovoltaic generator may have at least three output terminals (e.g., afirst series string of solar cells connected between first and secondoutput terminals, and a second series string of solar cells connectedbetween the second output terminal and a third output terminal). Thethree output terminals may, respectively, connect to the PV power device1603 over input terminals T_(in1), T_(in2), and T_(in3). As describedabove, if an unsafe condition, such as a grid-outage, overvoltage,undervoltage, a problem with the inverter (such as, but not limited to,the inverter described above with reference to power converter 900), orany other problem which may result in a potentially unsafe condition, ora failure in the single photovoltaic generator, is detected, controller1605 may turn on switch S16, short-circuiting the two of the terminalsof the single photovoltaic generator in order to protect, reduce therisk for, and so forth, power converter 1600 and/or personnel in thephysical proximity of PV power device 1603. When switch S16 is OFF, theoutput terminals of the single photovoltaic generator may be connectedin series to the input terminals of power converter 1600, (i.e., “normaloperation”) as described herein above.

In illustrative embodiments disclosed herein, photovoltaic generatorsare used as examples of power sources which may make use of the novelfeatures disclosed. Each PV generator may comprise one or more solarcells, one or more solar cell strings, one or more solar panels, one ormore solar shingles, or combinations thereof. In some embodiments, thepower sources may include batteries, flywheels, wind or hydroelectricturbines, fuel cells or other energy sources in addition to or insteadof photovoltaic panels. Systems, apparatuses and methods disclosedherein which use PV generators may be equally applicable to alternativesystems using additional power sources, and these alternative systemsare included in embodiments disclosed herein.

It is noted that various connections are set forth between elementsherein. These connections are described in general and, unless specifiedotherwise, may be direct or indirect; this specification is not intendedto be limiting in this respect. Further, elements of one embodiment maybe combined with elements from other embodiments in appropriatecombinations or subcombinations. For example, PV power device circuitryof one embodiments may be combined with and/or exchanged for powerdevice circuitry of a different embodiment. For example, transistor Q9of PV power device 903 may be disposed between electrical connections512 and 513 of junction box 511 and operated to short-circuit the inputto PV generator 101 of FIG. 5A.

1-25. (canceled)
 26. A safety switch comprising: a first connectorcomprising a first conductor; a second connector comprising a secondconductor; a switch circuit connected between the first conductor andthe second conductor, wherein the switch circuit is configurable into:an ON state that provides a direct-current serial path between the firstconductor and the second conductor, and an OFF state that disconnectsthe direct-current serial path; and circuitry connected between thefirst conductor and the second conductor and configured to: receivepower across the first and the second conductors; control, utilizing thepower, the switch circuit from the OFF state into the ON state; andcontrol, in response to a loss of the power, the switch circuit from theON state into the OFF state.
 27. The safety switch of claim 26, whereinthe circuitry is configured to receive the power at a first voltagebetween the first conductor and the second conductor when the switchcircuit is in the ON state, and receive the power at a second voltagebetween the first conductor and the second conductor when the switchcircuit is in the OFF state.
 28. The safety switch of claim 27, whereinthe circuitry is configured to maintain, while receiving the power, theswitch circuit in the ON state.
 29. The safety switch of claim 27,wherein the first voltage is between 15-200 millivolts when the switchcircuit is in the ON state, and the second voltage is greater than 25Vwhen the switch circuit is in the OFF state.
 30. The safety switch ofclaim 26, wherein: the circuitry is configured to receive one or morepower line communication signals transmitted to the safety switch viathe first conductor or the second conductor; and the control of theswitch circuit into the ON state is based on the circuitry receiving theone or more power line communication signals.
 31. The safety switch ofclaim 30, wherein the one or more power line communication signalscomprises an alternating-current signal over the first conductor or thesecond conductor.
 32. The safety switch of claim 26, wherein, when inthe ON state, the switch circuit has a current-voltage relationship thatcauses a voltage across the first and the second conductors to bebetween 15-200 millivolts when 10 amperes passes through thedirect-current serial path.
 33. The safety switch of claim 26, whereinthe switch circuit has an on-resistance that causes a second voltageacross the first and the second conductors to be generated in responseto a serial current from the first conductor to the second conductorthrough the direct-current serial path.
 34. The safety switch of claim26, further comprising a diode having a cathode connected to the firstconductor and an anode connected to the second conductor.
 35. The safetyswitch of claim 26, wherein: the circuitry is configured to receive thepower at a first voltage between 15-200 millivolts when the switchcircuit is in the ON state; the switch circuit comprises a transistorconnected, via a source or emitter terminal and a drain or collectorterminal, between the first and the second conductors; and the circuitryis configured to generate a control voltage between a gate or baseterminal of the transistor and the source or emitter terminal sufficientto maintain the switch circuit in the ON state.
 36. The safety switch ofclaim 35, wherein: the circuitry comprises a power circuit configured togenerate the control voltage from the first voltage, the control voltageis greater than the first voltage, and the power circuit is configuredto cease generating the control voltage based on: a serial currentflowing between the first and the second conductors through thedirect-current serial path falling below a threshold level, or receiptof a power line communication signal comprising a shutdown command. 37.The safety switch of claim 26, wherein the circuitry comprises anauxiliary power circuit configured to: receive the power from anauxiliary current flowing from the first conductor to the secondconductor through the auxiliary power circuit.
 38. The safety switch ofclaim 26, wherein the circuitry is configured to: receive a keep alivesignal via the first conductor or the second conductor; maintain theswitch circuit in the ON state based on receiving the keep alive signal;and control the switch circuit into the OFF state based on an absence ofthe keep alive signal.
 39. The safety switch of claim 38, wherein thekeep alive signal provides the power.
 40. The safety switch of claim 26,wherein the switch circuit comprises a transistor; and wherein thecircuitry comprises: a communication circuit configured to receive powerline communication signals on the first conductor or the secondconductor; an auxiliary power circuit configured to convert the power toconverted power; and a controller circuit configured to: generate, fromthe converted power, a control voltage on a gate or base terminal of thetransistor, and based on the power line communication signals, vary thecontrol voltage to control the transistor into the ON state and into theOFF state.
 41. The safety switch of claim 40, wherein the controllercircuit is configured to, in response to the power line communicationsignals, toggle the control voltage between a first value of less than 1volt and a second value of greater than 5 volts.
 42. The safety switchof claim 26, wherein the safety switch comprises a transistor connectedbetween the first conductor and the second conductor; and the circuitrycomprises an auxiliary power circuit configured to convert adrain-to-source or collector-to-emitter voltage across the transistor toa gate-to-source or base-to-emitter voltage applied to a gate or baseterminal of the transistor, wherein the gate-to-source orbase-to-emitter voltage is greater than the drain-to-source orcollector-to-emitter voltage.
 43. The safety switch of claim 26, furthercomprising a resistor connected between the first conductor and thesecond conductor and in parallel with the switch circuit.
 44. The safetyswitch of claim 26, wherein the first conductor is configured to beconnected to a photovoltaic panel connected to a power device, whereinthe power device is configured to, based on a change in current flowingthrough the safety switch, cease drawing power from the photovoltaicpanel to turn the safety switch to the OFF state.
 45. The safety switchof claim 26, wherein the switching circuit comprises a transistor thatprovides the direct-current serial path, and wherein the circuitry isconnected in across the transistor.
 46. A system comprising: aphotovoltaic string comprising a pair of photovoltaic panels coupled inseries through a safety switch; wherein the safety switch is connectedinline between the pair of photovoltaic panels; wherein the safetyswitch has an ON state that provides a direct-current serial pathbetween the pair of photovoltaic panels, and an OFF state thatdisconnects the direct-current serial path; and wherein the safetyswitch comprises circuitry configured to: receive auxiliary powerthrough the photovoltaic string, utilize the auxiliary power to controlthe safety switch from the OFF state to the ON state, and in response toa loss of the auxiliary power, control the safety switch from the ONstate to the OFF state; and a power device comprising: a power converterhaving inputs connected across the photovoltaic string, and a controlcircuit configured to control photovoltaic power generated by the pairof photovoltaic panels.
 47. A method comprising: receiving, betweenfirst and second conductors of a safety switch, power; controlling,utilizing the power, the safety switch to an ON state that provides adirect-current serial path between the first and the second conductors;and controlling, in response to a loss of the power, the safety switchinto the OFF state that disconnects the direct-current serial path. 48.A method comprising: receiving, at an output of a power converter, afirst power line communication signal indicating for the power converterto shut down; controlling, based on receiving the first power linecommunication signal, the power converter from a first mode of operationthat extracts photovoltaic power from a photovoltaic string according toa maximum power point tracking (MPPT) algorithm, to a second mode ofoperation that ceases to draw the photovoltaic power resulting in lossof photovoltaic current in the photovoltaic string, wherein thephotovoltaic string comprises a plurality of photovoltaic panels coupledin series through one or more safety switches, and wherein each safetyswitch of the one or more safety switches is connected inline between arespective adjacent pair of the plurality of photovoltaic panels; andcontrolling, in response to the loss of photovoltaic current, the one ormore safety switches from an ON state to an OFF state, wherein eachsafety switch of the one or more safety switches in the ON stateprovides a direct-current serial path between the respective adjacentpair of the plurality of photovoltaic panels to which the safety switchis connected, and in the OFF state disconnects the direct-current serialpath.